Design of a Solar-Powered Portable ECG Device with Optimal Power Consumption and High Accuracy Measurement

Round 1

Reviewer 1 Report

It is over-all a good scientific work but requires some improvements:

1) there is a bit of discrepancy between the abstract, the introduction and the paper itself. Reading the title I thought that the device was entirely powered by solar power. However, reading the paper is not clear to me if the device can sustain data connection/communication when powered only by solar with the aid of the super-cap.

2) full summary of results should be declared in the abstract and this include clear info about feasibility of full solar power as well as current consumption when transmitting the full ECG and current consumption for the connection phase (this can be very high).

3) the paper as it is written is too much centered on the BT connectivity however, is not clear to me if the BT protocol and firmware for the CPU have been optimized to deal with solar-power that is as steady as a battery

4) author should consider sharing production files as well as firmware

5) the introduction should include more references, below are some suggestions:

G. Gargiulo, P. Bifulco, R. A. Calvo, M. Cesarelli, C. Jin, and A. Van Schaik, "Mobile biomedical sensing with dry electrodes," in Intelligent Sensors, Sensor Networks and Information Processing, 2008. ISSNIP 2008. International Conference on, 2008, pp. 261-266: IEEE.

M. F. A. Rasid and B. Woodward, "Bluetooth Telemedicine Processor for Multichannel Biomedical Signal Transmission via Mobile Cellular Networks," IEEE TRANSACTIONS ON INFORMATION TECHNOLOGY IN BIOMEDICINE,, vol. 9, no. 1, 2005.

D. C. N. Golmie, O. Rebala, "Performance analysis of low rate wireless technologies for medical applications," Computer Communications, vol. 28, pp. 1266-1275, 2005.

A. V. a. J. Lekkala, "Wearable Wireless Biopotential Measurement Device," in Proceedings of the 26th Annual International Conference of the IEEE EMBS San Francisco, CA, USA, 2004.

G. D. Gargiulo, P. Bifulco, M. Cesarelli, A. Fratini, and M. Romano, "Problems in assessment of novel biopotential front-end with dry electrode: A brief review," Machines, vol. 2, no. 1, pp. 87-98, 2014.

As additional comment, have the authors considered to add activity monitoring as well to their device?

Author Response

Response to Reviewer 1 Comments

Point 1: there is a bit of discrepancy between the abstract, the introduction and the paper itself. Reading the title I thought that the device was entirely powered by solar power. However, reading the paper is not clear to me if the device can sustain data connection/communication when powered only by solar with the aid of the super-cap.

Response 1:

Thank you for your comment and suggestion.

We have had a number of edits to the abstract, 3.2. Testing ECG Signal and 5. Conclusions with content that fits perfectly with the article title that using solar energy is the main and unique energy source in this design.

In section 2.1.1 Solar energy harvesting and Figure 2: Solar energy harvesting and power modules we have shown that the IC BQ25570 generates 2 power sources 1.9V and 4.2V. 1.9V power is used to supply PIC16LF19186, ADS 1293 (digital module), and RN4020 source 4.2V for charging for supercapacitor and ADS1293 (analog module). When energy from solar panel IC BQ25570 will generate these 2 sources from solar penal energy. When there is no energy from solar panel IC BQ25570 will use energy on supercapacitor to generate 1.9V source

Point 2: full summary of results should be declared in the abstract and this include clear info about feasibility of full solar power as well as current consumption when transmitting the full ECG and current consumption for the connection phase (this can be very high).

Response 2:

Thank you very much for your comment.

In the abstract we have added more information about solar panel used in this design.

The parameters of the manufacturer BQ25570 can generate 110mA current which is a relatively large current for low power devices such as wearable devices and can meet many design requirements.

When the head voltage fluctuates IC BQ25570 will automatically use the power on the supercapacitor to compensate for this energy shortage.

In this design we use microchip RN4020 module with firmware mode MLDP V2. The optimization of energy consumption and connection maintenance has been supported by the manufacturer, which saves a lot of time for developers. In addition, we found that reducing the supply voltage to the module will reduce the current consumption many times.

Point 3: the paper as it is written is too much centered on the BT connectivity however, is not clear to me if the BT protocol and firmware for the CPU have been optimized to deal with solar-power that is as steady as a battery

Response 3:

Thank you for your comment

In section 2.1.3 Optimization power consumption, we present the energy optimization in the firmware of this design.

However, we found this section to be effective only with sampling frequency of 50 Hz or 100 Hz, with a higher sampling frequency due to the long duration of go to sleep mode and wakeup of PIC16LF19186 so it was ineffective, at this moment the part hardware requires continuous power supply.

Point 4:  author should consider sharing production files as well as firmware 

Response 4:

Thank you for your comment and suggestion.

We have included the firmware of the design (ECG_Board_Paper.rar)

Software Program: MPLABX IDE (v5.10)

Compiler: MPLAB XC8 (v2.05)

MPLAB Code Configurator v3 (MCC)

Programmer/ Debugger: MPLAB ICD4

Point 5: the introduction should include more references, below are some suggestions:

Response 5:

Thank you for your comments that are very helpful for me.

After reviewing papers were introduced by reviewer 1, we found that these articles were quite obsolete for most of the past 10 years. In this paper, we want to optimize the hardware so we use many new chips that integrate many features provided by the chip manufacturers. Most new chips have integrated many modules, making it easy to optimize the design.

In addition, we have cited many articles in the introduction according to recommend from the reviewer 1

We proceeded to edit the introduction according to the recommendation of the reviewer 1

Author Response File: Author Response.docx

Reviewer 2 Report

This manuscript has proposed a design of a portable ECG device by focusing on the optimal power consumption and high accuracy measurement. The design of the circuit part is excellent. The novelty in this manuscript is significant. The power consumption is well optimized according to the different modes of main components.

However, in the data treatment part. I think there are some points which should be improved. In the filter part, the authors have proposed to use a FIR filter. The name of FIR is not given (Butterworth, Chebyshev, Bessel, Gauss ,etc.). The order of filter should be given as well. As for the high pass filter with a frequency of 0Hz to 10Hz, I don’t think that it is adaptive for ECG analysis, especially for the HRV analysis. Normally, we eliminate the noise less than 0.05Hz or 0.04Hz.

The state of the subject during the ECG measurement is not described. They are in sit position? Before the ECG measurement, what have they done in order to get a rest state?

Author Response

Response to Reviewer 2 Comments

Point 1: However, in the data treatment part. I think there are some points which should be improved. In the filter part, the authors have proposed to use a FIR filter. The name of FIR is not given (Butterworth, Chebyshev, Bessel, Gauss ,etc.). The order of filter should be given as well. As for the high pass filter with a frequency of 0Hz to 10Hz, I don’t think that it is adaptive for ECG analysis, especially for the HRV analysis. Normally, we eliminate the noise less than 0.05Hz or 0.04Hz.

The state of the subject during the ECG measurement is not described. They are in sit position? Before the ECG measurement, what have they done in order to get a rest state?

Response 1:

Thank you for your comments that are very helpful for me.

We have updated ECG signal measurement status to section 3.2. Testing ECG Signal.

In the process of testing volunteers were in a state of sitting and leaning back on their chairs. This posture is quite comfortable for working.

In section 3.2. Testing ECG Signal we have updated more detail about testing signal and filter.

In this design, we focused on how to optimize power consumption for wearable devices, we did it by lowering the supply voltage for the components as well as optimizing operation in the firmware. This is also very consistent with the trend of reducing the operating voltage to reduce the power consumption of chip manufacturers around the world. As we discussed in Table 9. Used time of ECG device with differences sources, the working time of this design when there is no solar energy is only 2s. For other volunteers, activities such as running, or jumping will affect the power supply of solar panel, leading to a loss of stability. In Table 9, we also flew more about the test results of the device when replacing solar panel with 2 other battery sources. This is also an important suggestion for readers about the versatility of this design, which can easily change power energy without changing hardware.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Table 9 should report the light power that allow indefinite use of the system with no battery. From the text I gather that this is 30 W, is this correct? if So this is an important info to be given to the readers.

Author Response

Response to Reviewer 1 Comments

Point 1: Table 9 should report the light power that allow indefinite use of the system with no battery. From the text I gather that this is 30 W, is this correct? if So this is an important info to be given to the readers.

Response 1:

Thank you for your comment and suggestion.

In the picture we describe how we tested the ECG device, the light source is a lamp with power 27 W (that is the parameter from manufacture) and we changed this parameter in manuscript. However, we do not recommend using this light source in the experiment because it is quite old and sold only in Korea.

Currently there are many other light sources using LED technology with stronger light intensity and lower power that can be used in tests with solar energy.

Author Response File: Author Response.pdf